Titres of parasite-specific IgE were investigated in 19 patients thought to have recurrent, acute urticaria caused by sensitization to Anisakis simplex (Dujardin, 1845), before and after they were placed on a fish-free diet. Patients with other allergic disease and those being treated with corticosteroids or antihistaminics were excluded. Skin-prick tests were carried out with A. simplex extract, and blue- and white-fish extracts. The CAP system (Pharmacia), a commercial test kit developed for the assay of food-specific IgE, was used to monitor serum concentrations of total IgE and antigen-specific IgE against Anisakis, Ascaris, Echinococcus, Toxocara, tuna, salmon, shrimp, mussel and cod. Before going on a fish-free diet, the 19 patients had CAP scores against A. simplex of 5 (three cases), 3 (seven) or 2 (nine). After a mean of 120 days on the diet, the scores against A. simplex were unchanged in 15 of the cases, reduced in three [from 5 to 4 (one case) or from 2 to 0 (two cases)] and increased in one (from 2 to 3). Most (16) of the patients no longer had any urticaria and the others reported significant reductions in the intensity and frequency of their symptoms.